The present invention relates to a clutch unit used in a reduction-drive device, and a vehicle having the clutch unit.
An electromagnetic clutch using a multiplicity of friction plates is known as a conventional clutch unit for a differential-drive device. The differential-drive device has a reduction mechanism and a differential (differential device). The electromagnetic clutch is provided between the reduction mechanism and the differential in the differential-drive device, and changeovers a torque transmission and torque cutoff between the reduction mechanism and the differential.
Accordingly, if the electromagnetic clutch is in a torque transmitting state, as the driving source is driven for generating driving torque, the torque which has been decelerate through the reduction mechanism is transmitted to the differential through the electromagnetic clutch. The torque is transmitted from the differential to the left and right axle shafts.
When the driving source is stopped, the electromagnetic clutch is changed over to a torque cutoff state. In this state of changeover, even if the wheel-side rotation is transmitted to the differential, the rotation is not transmitted to the reduction mechanism and the driving source. For this reason, when the output of the driving source is stopped, the reduction mechanism and the driving source are prevented from being forcibly driven by the wheel-side rotation.
However, in the case of a configuration in which a changeover of transmission and cutoff of torque is effected by the electromagnetic clutch, there is a problem in that the torque transmitting capacity is small. If an attempt is made to enlarge the torque transmitting capacity of the electromagnetic clutch, the electromagnetic clutch becomes large in size, and there are problems in that the weight becomes large, and that the cost becomes high.
In addition, in the case of the electromagnetic clutch using a multiplicity of friction plates, even if the electromagnetic clutch is set in a cutoff state, there is a possibility of the occurrence of a large drag torque due to the viscosity of oil and the like. The larger the electromagnetic clutch, the more this drag torque increases, so that an increase in the torque transmitting capacity of the electromagnetic clutch is limited.
Therefore, it is a object of the invention to provide a clutch unit in which a torque transmitting capacity is large, and any drag torque does not occur.